Patent US 4,669,308

There is provided a method of determining the total inflow of a liquid through a liquid-flow system such as a sewage pumping station, in which liquid enters a sump cavity and is pumped out of the sump cavity on a periodic basis. The probable inflow rate during each pumping cycle is derived by first determining the true inflow rate prior to the beginning of a pumping cycle and extrapolating its trend forward through the time of the pumping cycle to arrive at a first calculated inflow rate, then determining the true inflow rate after the end of a pumping cycle and extrapolating its trend backward through the time of the pumping cycle to arrive at a second calculated inflow rate, and averaging the first and second calculated inflow rates to obtain the probable inflow rate during the pumping cycle. This latter rate is then multiplied by the time during which pumping takes place to yield an inflow during pumping, and this amount is added to the sump volume for each complete cycle.